Abstract Summary
In his Essay Concerning Human Understanding John Locke gives two explanations of intellectual habits and the association of ideas, one a psychophysiological account that has its origins in the Cartesian science of the brain, and the other a purely psychological account that seems to be original with Locke himself. After laying out Locke’s two positions and showing how each fits into the larger project of the Essay, we trace them the first to Locke’s reading of Nicholas Malebranche’s Recherche de la Vérité and ultimately to Descartes’ Traité de l’homme. These models explain habit and association in terms of the flow of nervous fluids creating traces in the brain. The second explanation is based on the speed with which ideas pass through the mind after frequent repetition. Locke uses it to explain why we falsely believe that we “see” three dimensionality. This psychological explanation was taken up by George Berkeley in his New Theory of Vision, and by other 18th-century writers. However, the psychophysiological explanation also persisted throughout this period among both philosophers and medical writers including Hermann Boerhaave and Albrecht Haller. An alternate psychophysiological explanation briefly flourished based on the Queries at the end of Newton’s Optics, and adopted by David Hartley in his Observations on Man. Nevertheless, it was the Cartesian brain-trace explanation which predominated throughout this period, and is even to be found at the end of the nineteenth-century in William James’ discussion of habit and association in his Principles of Psychology.
